1. Field of the Invention
This invention relates to the apparatus and method for processing polyurethane foams to form bicycle tires and the like.
2. Prior Art
For a number of years polyurethane foams have been used to produce products having outer integral skins that surround or partially surround a foam core. In such earlier developments, it has been recognized that bicycle and wheelchair tires can be, and in practice have been, produced from such foams to have an outer integral skin, and a foam core. Such products have gained acceptance because they give a ride that is rather comparable to pneumatic tires while not being subject to air loss, blow outs, and the like. Examples of such earlier developments are shown in U.S. patents of two of the inventors, U.S. Pat. Nos. 4,943,223 and 4,855,096, that the apparatus and method of the present invention improves upon to provide a tire of consistent quality with an appropriate density, and of minimum weight and resistance to rolling.
The present invention, unique from earlier technology, provides an apparatus and method that is useable for the production of non pneumatic tires and other products that will have a uniform density variability from the outer circumference to the inner diameter, providing ride comfort that is comparable to that of a pneumatic tire with greater wear life than pneumatic tires and is not subject to puncture or blow out.
In the past, solid and cellular polyurethane tires, semi pneumatic polyurethane tires, solid rubber tires and solid tires made from various other materials have been developed as set out in the above cited U.S. patents of two of the inventors and by others. Examples of such earlier apparatus and processes for spin casting items from liquid elastomers are shown in a number of earlier U.S. Pat. Nos. 3,200,180; 3,505,437; 3,751,551; 3,956,448; 4,049,767; 4,379,104; 4,387,070; 4,416,841; 4,472,340; 4,478,567; and 4,479,769, and in Canadian Patents No.'s 875,065 and 1,092,296. Additionally, non-pneumatic tires, and the like, preferably formed utilizing rotational or spin casting processes are shown in another U.S. Pat. No. 5,086,815 to two of the present inventors, and in U.S. Pat. Nos. 3,348,597; 3,605,848 and Canadian Patent No. 1,032,445, with a patent to Pointer, U.S. Pat. No. 4,436,128, showing a tubeless tire that is preferably formed from a polyurethane material and includes a thermoplastic cord formed in the tire bead for reinforcing that bead that the invention improves upon by a utilization of a continuous cord fitted therein in the molding process that is preferably formed as a continuous metal wire, providing uniform support at all points around the tire bead with little or no stretch.
While the above cited prior art shows that polyurethane foams have heretofore been used for producing tires, and the like, such have not provided molded items that are free of variations in density throughout a finished product. Further, such earlier apparatus and methods have produced tires, and the like, with voids and blemishes, in the product surface, which defects have greatly limited the market acceptance of such products. Additionally, other defects that non pneumatic tires have exhibited in a use and practice of earlier apparatus and methods are addressed and solved by the present invention to include a production of a tire that will remain securely attached to the rim over time and, in use, will maintain a proper circumference during use. Further unique to the invention, a tire manufactured using the apparatus and by the process of the invention will include a center line rib to decrease resistance to rolling, and a shoulder lug and improve off road traction over earlier designs, and provides for an improvement in static spring rate by closely controlling of the density of the foam as is preferably used in the tire manufacture to dramatically improve tire spring rate and the rolling resistance. Also, as an improvement over prior tire designs, the invention addresses and solves the problem of a non reliance of the tire outer skin in relationship to its inner core by dispensing with a utilization of a skinning foam like earlier tires have incorporated, thereby yielding an improvement in cell structure and density of the molded item. A tire is thereby provided that exhibits a higher density around its outer diameter, or tread surface, as compared to a somewhat lower but controlled density around its inside diameter.